Deposition of polystyrene microplastics on bare or biofilm-coated silica analysed via QCM-D

Electrophoresis and Quartz Crystal Microbalance Instrumentation to Sense Nanoplastics in Water

We report a Technical Note on detecting nanoplastics in water samples through electrophoresis and quartz crystal microbalance (QCM) instrumentation. We conducted electrophoresis experiments by immersing a QCM in a sample of ultrapure water containing polyethylene (PE) nanoplastics. It was interesting to observe that nanoplastics were attracted toward the QCM and adhered to one side of the QCM electrode. The attached particles introduced mass loading to the QCM and were characterized by a decrease in resonance frequency of the crystal. Furthermore, when a small region around the center of electrode was alone exposed for direct contact in water and the rest of the electrode was masked using photoresist, the nanoplastics were concentrated only in the exposed electrode region, significantly enhancing detection sensitivity. To further investigate the applicability for real-life water samples, we experimented with the technique with readily available bottled drinking water and mineral water, where we spiked these water samples with nanoplastics. It was observed that the resonance frequency shifts were significantly larger for samples with nanoplastics compared to samples without nanoplastics. In addition, Raman spectroscopy and microscopy imaging were used to further confirm the presence and locations of nanoplastics on the electrode surface. This study highlights the combination of electrophoresis and QCM effectiveness in detecting nanoplastics across different water types and their potential for broader applications in environmental monitoring.

Evaluation of the migration behaviour of microplastics as emerging pollutants in freshwater environments

Microplastics, as an emerging pollutant, are widely distributed in freshwater environments such as rivers and lakes, posing immeasurable potential risks to aquatic ecosystems and human health. The migration behaviour of microplastics can exacerbate the degree or scope of risk. A complete understanding of the migration behaviour of microplastics in freshwater environments, such as rivers and lakes, can help assess the state of occurrence and environmental risk of microplastics and provide a theoretical basis for microplastic pollution control. Firstly, this review presents the hazards of microplastics in freshwater environments and the current research focus. Then, this review systematically describes the migration behaviours of microplastics, such as aggregation, horizontal transport, sedimentation, infiltration, stranding, resuspension, bed load, and the affecting factors. These migration behaviours are influenced by the nature of the microplastics themselves (shape, size, density, surface modifications, ageing), environmental conditions (ionic strength, cation type, pH, co-existing pollutants, rainfall, flow regime), biology (vegetation, microbes, fish), etc. They can occur cyclically or can end spontaneously. Finally, an outlook for future research is given.

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl2 solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62-1.00 in NaCl and 0.48-0.96 in CaCl2) were higher than those for pear- and peanut-shaped MPs (0.01-0.63 in NaCl and 0.02-0.46 in CaCl2, and 0.01-0.59 in NaCl and 0.02-0.40 in CaCl2, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

Interactions between microplastics and contaminants: A review focusing on the effect of aging process

Microplastics (MPs) in the environment are a major global concern due to their persistent nature and wide distribution. The aging of MPs is influenced by several processes including photodegradation, thermal degradation, biodegradation and mechanical fragmentation, which affect their interaction with contaminants. This comprehensive review aims to summarize the aging process of MPs and the factors that impact their aging, and to discuss the effects of aging on the interaction of MPs with contaminants. A range of characterization methods that can effectively elucidate the mechanistic processes of these interactions are outlined. The rate and extent of MPs aging are influenced by their physicochemical properties and other environmental factors, which ultimately affect the adsorption and aggregation of aged MPs with environmental contaminants. Pollutants such as heavy metals, organic matter and microorganisms have a tendency to accumulate on MPs through adsorption and the interactions between them impact their environmental behavior. Aging enhances the specific surface area and oxygen-containing functional groups of MPs, thereby affecting the mechanism of interaction between MPs and contaminants. To obtain a more comprehensive understanding of how aging affects the interactions, this review also provides an overview of the mechanisms by which MPs interact with contaminants. In the future, there should be further in-depth studies of the potential hazards of aged MPs in different environments e.g., soil, sediment, aquatic environment, and effects of their interaction with environmental pollutants on human health and ecology.